The present invention relates to a vacuum suspension for hoisting plates, especially large size concrete plates which are still not fully hardened and brittle, or other plates exhibiting similar properties.
In known prior art equipment employing vacuum suspension for handling a hoisted body by suction, vacuum pumps create the necessary underpressure. These suspensions are mostly built as structures consisting of tubes simultaneously utilized as a vacuum chamber, and they operate by suction cups which are movably attached or affixed to the carrying structure and connected by flexible pipes to vacuum containing members. However, the suction cups are oriented and controlled by hand. Experiments have been carried out to employ self controlled valves for connecting the suction cups with vacuum chamber. Thus, the known solutions have following disadvantages:
1. The structure form limits the number of suction cups and results in a strong underpressure necessary to obtain adequately high suction forces.
2. High unitary suction forces, spaced widely one from the other on the surface of a hoisted body, may spoil a still not hardened plate during lifting, causing either a three dimensional deformation or direct destruction.
3. When handling different sizes of plates, especially with perforations /e.g. doors, windows etc./, a manual arrangement of suction cups for each plate kind requires additional work and time.
4. When suction cups of constant arrangement operate by ball valves, besides being expensive, the structure is very sensitive to dirt, has comparatively high inertia in time, so they can leak or fail to operate at all.
5. This rather complicated structure requires a strong vacuum and due to low reliability of ball valves leakage occurs and in turn break downs result. The necessary repair work is rather difficult and expensive due to high power pumps kept almost in steady operation.
6. The necessary vacuum for the requisite suction forces depends only on the pump yield, thus being of relatively low dynamic characteristic causing the work reliability to decrease.